Please excuse this stupid question. I’ve never been to Chicago, but very well may end up moving there for a job next year. I’ve been looking at some neighborhood maps around the Lakeview and surrounding areas.
It looks like North Lakeview Drive is a very busy highway which separates the residential areas from the lake. Are there pedestrian bridges or any easy way to reach the lake if you’re say around the area at W Roscoe Street and North Broadway and start walking east?
There are underpasses with sidewalks. There is one overpass but its down by lincoln park zoo.
That’s the only one I can think of, too (it’s near North Avenue, IIRC). Most, if not all, of the streets which actually intersect with North LSD do so with highway-style entrance and exit ramps, and the surface street itself passes under LSD. As MikeG notes, most of these would have sidewalks as part of the underpass.
Looking at Google Street View now, and the intersection you described (Roscoe and Broadway), you can walk under LSD at Belmont (which is 3 blocks south of Roscoe).
Are these underpasses safe to walk? I like the idea of having the lake close, so I’d like to be able to walk over and spend some time there. Is this common among people in the area?
As safe as any sidewalk in the city :).
The land between LSD and the lake itself is city park land (there’s a well-known path that runs parallel to LSD in the park area), and you’ll find a ton of people going there to run, bicycle, rollerblade, etc. They’re undoubtedly using those underpasses to get to and from the park areas.
You can take a look for yourself: go to Google Maps, go to the corner of Belmont and Sheridan, and go to Street View. The sidewalk part of the underpass is on the north side of Belmont, is quite wide, and is separated from the street itself by a concrete barrier. Personally, I wouldn’t think twice about using it.
Yes, tens of thousands of people use the underpasses every day in the summer. They are busy with cars and well lit so your chances of being murdered while walking the 50 yards or so, your body dismembered, and then dumped in the bushes are low.
You don’t have to cross at Belmont. There is a pedestrian underpass right by Roscoe. I can’t remember exactly which street, but I used to live on Aldine (block south of Roscoe) and there is one right around there, maybe a block north of Roscoe?
Looks like it’s a little further than that, around Cornelia? If you look on Google Maps (not the street view) you’ll see a little indicator of a pedestrian path that “emerges” from the east side of Lake Shore Drive across from Cornelia. (Tried to find it on street view, but it’s not clear. The entrance to the underpass is on the east side of inner Lake Shore Drive. I don’t recall there being a sign or anything, you kind of have to keep an eye out for it.)
To the OP–you DO realize that “summer” is July and August? 
**North side crossings of Lake Shore Drive:
**Chicago underpass
Oak underpass
Division underpass
North underpass
LaSalle Drive underpass (street)
Pasarelle at 1800 N
Fullerton underpass (street)
Diversey underpass
Barry underpass
Belmont underpass (street)
Roscoe underpass
Addison underpass
Waveland underpass
Irving Park underpass (street)
Junior Terrace underpass
Montrose underpass (street)
Wilson underpass (street)
Lawrence underpass (street)
Argyle underpass
Foster underpass (street)
Berwyn underpass
Bryn Mawr underpass (street)
Lakefront access is detailed on my Chicago bikemap, which is online at http://www.chicagobikemap.com
What? Summer doesn’t start in March and end in October? 
Summer is beautiful in Chicago. Especially on those rare years where it falls on a weekend!
Oh, the summers are long enough (and too hot and damned humid. Christ, do I hate sweltering Chicago summers.) It’s the springs that are too short-lived, IMHO.